This invention relates to an alloy filter for providing improved contrast resolution in a camera for recording gamma rays, e.g. a planar or tomographic camera.
The invention disclosed and claimed herein was first disclosed in Disclosure Document No. 150133 filed at the U.S. Patent and Trade Mark Office on May 9th 1986.
Tomography is an increasingly widely used technique for providing images of internal organs. In this technique, a patient is fed a pharmaceutical substance labelled with a radionuclide, which substance collects preferentially in the organ to be examined, for example the liver or the lung. The radionuclide emits gamma rays from which an image is formed by a gamma-ray camera. This usually comprises a flat scintillating crystal, usually of sodium iodide, behind a collimator in the form of a perforated lead plate or the like. The sodium iodide crystal scintillates whenever it receives a gamma ray having a predetermined minimum energy, and the scintillations are detected by a battery of photomultipliers behind the crystal. Signals from the photomultipliers are then digitised and an image of the organ being examined is constructed from the digitised signals, generally over an exposure time of a few minutes.